Objectives: Proteinuria is regarded as a critical marker of kidney damage with and without diabetes. As a marker of inflammatory response and endothelial dysfunction, we aimed to evaluate the impact of proteinuria on the development of new-onset diabetes according to the kidney function among the young adult population. Methods: We used data from the 6,891,399 subjects aged ≥20 and <40 years old of National Health Insurance Service (NHIS) between 2009-2012. Subjects without history of diabetes or impaired glucose tolerance (IGT) were extracted. We defined the exposure as a dipstick proteinuria ≥1+. The primary was new-onset diabetes. We used a multivariate Cox-proportional hazard model to identify the impact of proteinuria on new-onset diabetes. We performed subgroup analysis according to the status of metabolic syndrome. Results: A total of 5,383,779 subjects were included in the study. The mean age was 30.56±4.98 years old, there were 81,237 (1.53%) subjects with proteinuria. During 7.32±1.16 years, 62,148 (1.15%) subjects were diagnosed with new-onset diabetes. Presence of proteinuria significantly increased risk of diabetes (adjusted hazard ratio [aHR] 1.62, 95% confidence interval [CI] 1.55, 1.70) after adjustment with age, sex, anthropometric data, physical exercise status, serum glucose, and total cholesterol.  Presence of metabolic syndrome significantly increased risk of diabetes over 4.5 times. Also, in subjects with only two components of metabolic syndrome increased risk of diabetes (aHR 2.5, 95% CI 2.13, 2.97). Among each component of metabolic syndrome, presence of hypertriglyceridemia most increased risk of diabetes (aHR 2.02, 95% CI 1.81, 2.25)  Conclusions: Dipstick proteinuria is a significant risk factor for new-onset diabetes in young adult population. Close monitoring and evaluation of proteinuria is warranted for disease risk modification, especially in subjects with risk of metabolic syndrome.